Topology description has been moved to a separate Topology class

* For now it is still hardcoded, although it is a prelude for loading the topology from an external file by a parser
* But it enabled to make a "pass" command for sending the message to all neighbours of a node
* also, connect-test example has been updated (as always ;)
Support for gather messaging

* adds GatherRegistry which submits a message only after it has been obtained from a given number of nodes
* fixes memory problems with file name sanitization in log